Wire wrap screens are made by putting a series of longitudinal ribs in a circular arrangement an having each rib extend radially beyond a hub that places all the ribs in a cylindrical arrangement. A wrap wire is passed between the a weld roller and the ribs in succession as the hub rotates on its axis and the ribs are drawn along axes parallel to the axis of rotation of the hub. The weld roller is adjusted for the amount of force it places on the wrap wire. Current is applied as the wrap wire encounters a rib to effect a resistance weld.
The problem with this technique is that the wrap wire can neck down or get thinner as a result of uneven force applied to the wire from the weld roller. Additionally, if the wire is bent as it contacts a rib such bending also contributed to necking down when resistance welding the wrap wire to the ribs.
The present invention addresses this issue by straddling ribs with non-conductive and preferably ceramic supports so that the ribs extend radially only a fixed distance beyond the supports. This limits the penetration of the wire under pressure from the roller regardless of the roller force setting. As a result the penetration is uniform when the welding takes place. As an option, the wire can be pre-rolled to approximately the end diameter of the screen being made before there is rib contact as a way of reducing bending at the rib contact for the wire. This can be done with a set of opposed rollers through which the wire is fed before it contacts a rib mounted to the screen head. U.S. Pat. No. 3,875,977 is relevant to pre-rolling wrap wire.
These and other aspects of the present invention will become more readily apparent from the detailed description of the preferred embodiment and the associated drawings while recognizing that the full scope of the invention is given by the claims.